Fault interrupting devices are designed to trip in response to the detection of a fault condition at an AC load. The fault condition can result when a person comes into contact with the hot side of the AC load and an earth ground, a situation which can result in serious injury. A ground fault circuit interrupter (GFCI) detects this condition by using a sense transformer to detect an imbalance between the currents flowing in the line and neutral conductors of the AC supply, as will occur when some of the current on the load hot side is being diverted to ground. When such an imbalance is detected, a relay or circuit breaker within the GFCI device is immediately tripped to an open condition, thereby removing all power from the load.
Many types of GFCI devices are capable of being tripped not only by contact between the line side of the AC load and ground, but also by a connection between the neutral side of the AC load and ground. The latter type of connection, which may result from a defective load or from improper wiring, is potentially dangerous because it can prevent a conventional GFCI device from tripping at the required threshold level of differential current when a line-to-ground fault occurs.
A ground fault is not the only class of potentially dangerous abnormal operating conditions. Another type of undesirable operating condition occurs when an electrical arc jumps between two conductors or from one conductor to ground also known as an arcing path. This spark represents an electrical discharge through the air and is objectionable because heat is produced as an unintentional by-product of the arcing. Such arcing faults are a leading cause of electrical fires.
Arcing faults can occur in the same places that ground faults occur; in fact, a ground fault would be called an arcing fault if it resulted in an electrical discharge, or arc, across an air gap. A device known as an arc fault circuit interrupter (AFCI) can prevent many classes of arcing faults. Both GFCIs and AFCIs are referred to as fault protection devices.
Prior art self testing fault protection devices typically provide a self test which replaces a user having to perform manual tests at fixed periods of time, for example, weekly, monthly, and so on. Because the user relies on the self testing fault protection device to perform self-tests, the user may have a false sense of security. For example, many self testing fault protection devices only test for electronic operation and do not test for the opening and closing of contacts of the self testing fault protection device. If there is a defect with a component other than the electronics, a user can believe that the device is providing fault protection and can inadvertently be injured.
Also, as a solenoid of a fault protection device is operated over time, the semiconductor that is used to operate the solenoid can become degraded to a point where it approaches failure. This occurs because a 500 volt transient is placed across the transistor every time the solenoid is deenergized. Many manufacturers of fault protection devices place a diode between the solenoid and transistor. The diode is referred to as a suppressor diode. However, placing a suppressor diode across the solenoid or from the transistor collector to ground significantly lengthens the time to open contacts to break a conductive path. Since a life may be involved, time is of the essence regarding quickly opening the contacts of the fault protection device.
Another problem with conventional fault protection devices is that their load or feed-through terminals are hard wired to the face receptacles of the GFCI or AFCI. Therefore, if a user miswires the GFCI or AFCI by connecting the hot and neutral lines to the load terminals and equipment is plugged into the GFCI or AFCI via the face receptacles, the face receptacles can still be powered even if the GFCI or AFCI is in a tripped or off state. This can lead to potential injury to the user because the user would be under the impression that the GFCI or AFCI is in a tripped condition that always provides protection.
Still another problem with conventional fault protection devices is that electrical sparks associated with the input power line sometimes occur when the contacts of the protection device close. The high temperatures associated with the electrical sparks sometimes deteriorate the non-metallic housing of the protection device. Current solutions such as making the walls of the protection device thicker are not cost effective.
Thus, there is a need for a fault protection device which allows for a quick response in opening the contacts of the fault protection device without damaging the transistor or adding a delay in responding to a fault condition.
Still yet another need exists for a fault protection device that has face receptacles that are isolated from the load terminals.
Still another need exists for a fault protection device that allows the fault protection device to self-test without providing a momentary interruption in power to current sensitive equipment.
A further need exists for a structural housing that is resistant to burning or melting from the high temperatures related to electrical arcs. The structure should also provide an arrangement that maximizes space on a printed circuit board.